Probing the solvent shell with ¹⁹⁵Pt chemical shifts: Density functional theory molecular dynamics study of Pt^II and Pt ^IV Anionic Complexes in Aqueous Solution

Ab initio molecular dynamics (aiMD) simulations based on density functional theory (DFT) were performed on a set of five anionic platinum complexes in aqueous solution. ¹⁹⁵Pt nuclear magnetic shielding constants were computed with DFT as averages over the aiMD trajectories, using the two-component relativistic zeroth-order regular approximation (ZORA) in order to treat relativistic effects on the Pt shielding tensors. The chemical shifts obtained from the aiMD averages are in good agreement with experimental data. For Pt(II) and Pt(IV) halide complexes we found an intermediate solvent shell interacting with the complexes that causes pronounced solvent effects on the Pt chemical shifts. For these complexes, the magnitude of solvent effects on the Pt shielding constant can be correlated with the surface charge density. For square-planar Pt complexes the aiMD simulations also clearly demonstrate the influence of closely coordinated non-equatorial water molecules on the Pt chemical shift, relating the structure of the solution around the complex to the solvent effects on the metal NMR chemical shift. For the complex [Pt(CN) ₄]²-, the solvent effects on the Pt shielding constant are surprisingly small.